That sounds like a blood pressure issue. Are you holding your breath when performing the exercise?
It could well be a simple case of migraine headache coming on from to much time reading and has exposed itself on training day when you held your breath. There was a time I suffered from them because of to much computer usage at my old job. Ended up getting a stigmatism in my eye and needed to wear glasses for a year when reading from a computer etc.
If I were you I wouldn't worry to much, it is allot more comman than you think and if you generally feel OK than just back off from the high intensity for a week and less reading in general both books and computer.
If you are worried, see a doc, but I bet he will say the same thing mate.